To reproduce:

1. Open the project, attached by the tester (sceneReference.zip)
2. Open the "on" scene and add it to the Build settings
3. Add the "on" scene to Network Manager's Offline Scene and Online Scene fields
4. Open "arrg" scene and add it to the Build settings
5. Open the "on" scene, rename it to "not_on" and move it to temp folder
6. Rename the "arrg" scene to "on"
7. Try adding "on" scene to Network Manager's Offline Scene and Online Scene fields

Expected: user should be able to add a scene to the field after renaming it

Reproduced in 5.5.5p1, 5.6.3p2, 2017.1.0a5
Did not reproduce in 2017.1.0a6, 2017.1.2p1, 2017.2.0f3, 2017.3.0b5

Not reproducible since 2017.1.0a6